1. Field of the Invention
This invention relates to a shape extraction system and a 3-D (three dimension) information acquisition system using the shape extraction system, and more particularly to a shape extraction system which extracts the boundary of an object on the basis of a photographic image obtained in a state where background lighting is applied to the object whose two-dimensional image boundary is to be extracted and a photographic image obtained in a state where no background lighting is applied to the object and a 3-D information acquisition system which acquires 3-D information about the object by using the shape extraction system as component techniques.
2. Description of the Related Art
As for a conventional shape extraction system, Jpn. Pat. Appln. KOKAI Publication No. 11-73491 has disclosed an image cutout method using infrared rays as light of a specific wavelength outside the visible light region.
As another conventional shape extraction system, Jpn. Pat. Appln. KOKAI Publication No. 2000-224410 has disclosed a method of determining a cutout area by using a light source with a specific chroma and a specific lightness behind the object, or chromatic techniques.
As still another conventional shape extraction system, Jpn. Pat. Appln. KOKAI Publication No. 10-124704 has disclosed a 3-D information acquisition apparatus.
The 3-D information acquisition apparatus calculates a hypothetical existence area using the boundary between the object and the background in the image.
The hypothetical existence area is a conical area which has the projection center of the camera at the vertex and the shape of whose cross section is the boundary between the object and the background in the image.
The conical area (or hypothetical existence area) is written using a boxel (a model expressed by cubes of a specific size).
The above-described process is carried out repeatedly, as the object is turned through a specific angle by a turntable.
Then, a common hypothetical existence area is determined and 3-D information about the object is acquired.
The boundary between the object and the boundary in the image is determined from the difference between the image obtained by photographing only the background in the absence of the object and the image obtained by photographing the background in the presence of the object.
Since the image cutout method disclosed in Jpn. Pat. Appln. KOKAI Publication No. 11-73491 cuts out the silhouette of an image using infrared rays, the result of cutout might be influenced by the environmental condition, particularly the ambient temperature or the temperature of the object.
Furthermore, the image cutout method requires not only a special light source that emits infrared rays but also a special band-pass filter and a special photographing apparatus, resulting in the disadvantage of making the apparatus expansive.
On the other hand, in the cutout area determining method disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2000-224410 is at a disadvantage in that it is difficult to cut out accurately an object whose chroma is similar to that of the background.
Particularly in the cutout area determining method, when a part of the object is a metal surface (a flat metal surface or a scattering surface similar to this or a part with a relatively high reflectivity), the metal surface part looks the same color as that of the background as a result of reflecting the background (color). This causes the problem of the shape of the object to be recognized erroneously.
In the prior art 3-D information acquisition apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 10-124704, to improve the accuracy of 3-D information, it is necessary to make the specific angle smaller. This increases the number of shootings, causing the problem of increasing the photographing time.
In the 3-D information acquisition apparatus, to set the photographing angle first, the turntable turns and stops repeatedly. This applies acceleration to the object, which might cause the object to overturn or be deformed.
Furthermore, since the stop position of the 3-D information acquisition apparatus must be controlled with high accuracy, this leads to the disadvantages that the moving unit and control unit for the turntable are complex and expensive.
In the 3-D information acquisition apparatus, to determine the boundary between the object and the background in the image, the difference between the image of only the background and the image of the object with the background is used. Because the camera exposure, focus, and shutter speed vary from one shooting to another, this causes the problem that the boundary might not be determined with high accuracy.
Furthermore, in the 3-D information acquisition apparatus, since a common hypothetical existence area is determined directly by using a boxel model, the number of images necessary to determine whether a certain boxel is included in the common hypothetical existence area is large, which leads to the disadvantage that the processing time is very long.
Moreover, in the 3-D information acquisition apparatus, since it is necessary to store the probability of existence related to each of the boxels in the previously set boxel model, this results in the disadvantage that the memory capacity must be very high.